/*
 * Copyright (c) 2008 Cameron Zemek
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */
package net.zeminvaders.lang;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;

/**
 * Wraps a Reader to provide peeking into the character stream.
 *
 * @author <a href="mailto:grom@zeminvaders.net">Cameron Zemek</a>
 */
public class PeekReader {
    private Reader in;
    private CharBuffer peakBuffer;

    public PeekReader(Reader in, int peekLimit) throws IOException {
        if (!in.markSupported()) {
            // Wrap with buffered reader, since it supports marking
            in = new BufferedReader(in);
        }
        this.in = in;
        peakBuffer = CharBuffer.allocate(peekLimit);
        fillPeekBuffer();
    }

    public void close() throws IOException {
        in.close();
    }

    private void fillPeekBuffer() throws IOException {
        peakBuffer.clear();
        in.mark(peakBuffer.capacity());
        in.read(peakBuffer);
        in.reset();
        peakBuffer.flip();
    }

    public int read() throws IOException {
        int c = in.read();
        fillPeekBuffer();
        return c;
    }

    /**
     * Return a character that is further in the stream.
     *
     * @param lookAhead How far to look into the stream.
     * @return Character that is lookAhead characters into the stream.
     */
    public int peek(int lookAhead) {
        if (lookAhead < 1 || lookAhead > peakBuffer.capacity()) {
            throw new IndexOutOfBoundsException("lookAhead must be between 1 and " + peakBuffer.capacity());
        }
        if (lookAhead > peakBuffer.limit()) {
            return -1;
        }
        return peakBuffer.get(lookAhead - 1);
    }
}
